The present invention relates to a method for operating a four wheel drive-type transmission system of a motor vehicle. The invention also relates to a transmission system operating in this way. It also relates to a vehicle comprising such a transmission system. The invention relates finally to a computer program.
The invention applies to a vehicle equipped with a controlled four wheel drive transmission system (4×4). The objective of this type of vehicle is to enhance the services such as the behavior and drivability, particularly on take-off, that is to say when a vehicle is set in motion and when crossing an obstacle.
A transmission system of the fourwheel drive-type is known in which an electromagnetically controlled means for mechanically coupling a front axle to a rear axle (coupler) can operate according to three states defining three modes of operation of the transmission system,                a first transmission mode in which only a portion (variable) of the maximum torque capacity from a torque source (the engine of the motor vehicle) and intended for the rear axle system is effectively transmitted to the rear axle system; this first mode, called “automatic 4*4” mode, corresponding to a so-called “controlled” coupler, that is to say that a control system of the coupler automatically manages its operation, in particular the quantity of torque that is transmitted or transmissible,        a second transmission mode in which all of the maximum torque capacity from the torque source and intended for the rear axle system is actually transmitted to the rear axle system; this second mode, called “all-terrain 4*4”, mode corresponding to a so-called “closed” coupler, that is to say that it is locked in a state defining a fixed transmissible maximum torque value, the locking preferably being electrical,        a third transmission mode in which no torque (or a negligible torque) from the torque source is transmitted to the rear axle system; this third mode, called “4*2” mode, corresponding to a so-called “open” coupler, that is to say that the coupler is deactivated or that it transmits only a negligible quantity of torque.        
Thus, the driver should know the functional state of the current 4×4 mode of the vehicle from the basis of his or her interaction with the 4×4 mode selection button. The vehicle has to be able to also communicate to the driver certain information such as, for example, elevated heating-up of the 4×4 coupler or the failure of the 4×4 system. The system also has to be able to check the compatibility of the speed and temperature conditions applied to the coupler. Thus, there is a need for a man-machine interface (MMI) device and for the interpretation of the driver's demand to be applied to a vehicle equipped with a 4×4 transmission system.
The document FR2885427 discloses a device for monitoring and/or controlling equipment of a motor vehicle with push buttons and a touch pad.
The document WO 99/20483 discloses an equipment control button on a dashboard of a powered vehicle.